Method of and means for recovering metalliferous minerals by flotation.



GA. CRERAR.

METHOD-0F AND MEANS FOR RECOVERING METALLIFEROUS MINERALS BY FLOTATIN.

APPLICATION FILED MAR19. 1915. RENEWEDNOV. 27.1916.

'Patent-ed July 10,1917.

GEORG-E CERAR, 0F SPOKAN E, WASHINGTON, ASSIGNOR OF SIXTY ONE-HUNDREDTHS TO JAMES L, BOYLE, 0F LOS ANGELES, CALIFORNIA.

METHOD 0F AND MEANS FOR RECOVERING METALLIFEOUS MINERALS BY FLOTATION.

Application led March 9, 1915, Serial No. 13,212.

To all whom t may concern.'

Be it known that I, GEORGE CRERAR, a citizen of the United States, residing at Spokane, in the county of Spokane and tion process.

The film or froth flotation method of separating and recovering the metallic or submetallic minerals from the earthy gangue minerals differs from the commonly known wet or gravity process of concentration, wherein the minerals are separated by taking advantage of their differences in specific gravity, in that the minerals are raised into and held in a body of froth on the surface of a body of ore pulp of a consistency of two or more of water to one of ore.

The necessary froth mixture is made by mixing with the ore during -the process of grindin in water or afterward, substances Vcalled rothing agents. These may be certain essential oils as yellow pine oil or oil eucalyptus, fatty acids as oleic acid, wood tars, tar oils, wood acids, turpentines, and other products obtained from the destructive distillation of both hard and soft woods, crude fresh coal tar and products from the destructive distillation of tar as gas works light oil, creosote oil, creosol, phenol, etc.

oped by films; making where permitted, a.

body of froth of thickness varying with the kinds and amounts of frothing agents, the

Specification of Letters Patent.

Patented July 10, 1917.

Renewed November 27, 1916. Serial No. 133,984.

consistency and nature of the pulp, and the quantity of air and method of aerating the pulp mixture. The film enveloped bubbles on reaching the surface now form the body Which may properly be called froth.

The metallic or sub-metallic minerals such as sulfids, sulf-arsenids, sulf-antimonids, telurids and native gold, silver and copper possess the property of attaching themselves to the film envelops of the rising bubbles either through adhesion of the minerals to the film substance envelops on being dried or partly dried by the air or gas contained within or through the affinity of the minerals for the air or gas within the filmsubstance envelop.

Bubbles on the surface of the froth body are constantly breaking from the expansion of the gases within or other causes and droppingtheir load of minerals on those coming up below, thus automatically enriching the top of the froth body. The enf riched surface in practice is skimmed continuously into launders provided for the purpose of receiving the concentrate.

There are two processes of froth flotation in common use at this time.

.The first and perhaps the older process consists essentially in beating or churning air and frothing agent simultaneously into a comparatively large body of pulp mixture. This pulp mixture with entrained air bubbles passes into a. spitz-kasten where the bubbles rise to the surface carrying the minerals into the froth body on the-surface Where the top portion is skimmed mechanically into a launder where the froth is broken up ba spray and the concentrate thus liberate sluiced away to tanks or other means of handling same.

The second method consists essentially in blowing air up through the pulp mixture through a porous medium forming the top part of an air compartment or compartments and the bottom of the tank or cell containing the pulp mixture. The bubbles rising to the surface 'of the liquid produce froth and carry concentrate into the froth body on the surface as in the first process,

The enriched surface of the froth is removed continuously by overflowing into launders provided along the sides of the rectangular cells andia launder around the top of the round cells.

Typical of the irst (mechanical process) is the ballot machine and .the practice ofthe Minerals. Separation Company; and of the second (pneumatic process) are the Callow and the Flynn-Towne machines and processes.

In .using the above processes, principally on account of the comparatively large liquid body of pulp mixture in more or less violent agitation in the machines, particles of mineral that may have been'caught by the films of the rising bubbles become wetted again and joinmthe'gangue minerals and thus pass into t-he tailing. Tailing from botht the mechanical and pneumatic process machines contain appreciable amounts of loatable minerals.

With a view to improving the present practice of froth flotation I have invented what may be called a dry froth flotation process and a machine for utilizing same. The name dry froth flotation is selected for the reason there is no body of pulp mixture, such as is maintained in the foregoing processes and machines.

The new process may be carried out by mixing a suitable frothing agent or agents with the ore pulp at the head of the mill or with the dry ore going into the mill on a conveyer belt or with the ore stream passing through an elevator or with the ore stream passing into a ball or pebble mill in such a way that the proportion or frothing agent to ore is so maintained that the frothing agent is mixed thoroughly with the pulp, and sucient time allowed for them to become assimulated with the necessary constitnents of the gangue to form the desired mineral collecting films or froth. The ore should under ordinary conditions of operation be ground to pass a 48 mesh screen.

I have discovered -that by spreading the frothable pulp mixture out over a porous deck which may be made of canvas, porous brick or any other suitable porous material Well known as suitable for analogous purposes through which air is forced, a greater proportion, of the loatable metallferous minerals will be floated and can be recovered than by previous methods.

The novel apparatus involved in this invention and discovery includes the combination of a sloping porous deck, means to distribute and spread the pulp froth mixture over the deck at an upper level, a skimming Wall located in the way of the froth and having its top below7 the level of the upper part of the deck and means to drain away the froth at a considerable depth below the level of the skimming wall top so that the process may be automatically performed through the media of the apparatus and the forces of nature acting under direction thereof.

rIo condense this apparatus to cover minimum floor space for a. given capacity, a double deck form of apparatus is provided.

rIhe invention and discovery may be understood by reference to the accompanying drawings in connection with the following description.

In the drawings Figure l is an elevation partly in axial sectlon of an apparatus constructed in ac.- cordance with this invention and discovery and charged with air pressure and materials effecting treatment of the minerals according to the new method. y

Fig. 2 is a broken plan of the apparatus shown in Fig. 1, parts being broken away at different stages to expose dierent portions of theoperative parts.

'Ihe principle of this invention is the conversion of the pulp charged with a froth- Ving agent into froth and maintaining the same in a frothy condition until the separation of the metalliferous minerals has been effected, meantime causing a de-hydrn'ting action to take effect upon the surface of the metalliferous minerals; and an important feature of the discovery is that the froth must be produced by applying directly to the pulp a sufficient quantity of dry air to convert all such pulp into froth and that the presence of liquid not in the form of froth should be avoided until the separation of the metalliferous particles from the gangue and the mineral-carrying froth from the barren froth has been effected. That is to say in this new process the surfaces of the metalliferous mineral particles are dried and kept dried as fully as possible throughout the treatment.

The dehydrating and frothing eifecbmay lbe maintained to greater or less efficiency with variously constructed apparatus in accordance with the invention and discovery, and it is understood that the apparatus shown in said Figs. l and 2 is merely illustrative of what I at present regard as the best embodiment of the mechanioal means employed in carrying out the invention.

. In conducting the process with said apparatus, the pulp mixture 1 of a consistency of one and one-half or more of water to one of ore by weight and an appropriate amount of a suitable frothing agent mixed therewith is introduced through the distributer 2, 3, 4 to the upper end of the frothing deck 5 upon which said mixture is spread evenly at an upper level.

The apparatus shown is of the plural deck construction, the upper deck 5 being of conical form and porous, the material of which may be of any suitable character of sufficient porosity to deliver air therethrough in minute or very finely divided closely-associated currents, so that the liquid material spread over the apex or upper end of the conical deck will immediately be transformed at this higher level into froth and owing to the slopeof said deck will gravitate away from the source of supply at the distributor. Said porous deck is supported by joists 6 and is superposed above air compartments 7 the lower walls of which are formed by an impermeable floor 8 underneath said joists an outer wall 9, which in the form shown is annular, and a collar 10 fixed to the top of an air pipe l1 that is connected through a valve 12 and pipe 13 with a source of compressed air. The several compartments 7 are united by collar 10 which forms the bottom of a'central compartment 14 formed beneath the bottom of the distributor and causes an intercommunication of air throughout the compartments 7, so that compressed air passing through the central air distributer chamber 14 is equally distributed to all the compartments. The air pipe 11 may be constructed to constitute a standard for the central flanged collar 10 that forms the bottom of the air chamber 14 and a support for the upper ends of the floor 8, and a furthersupport for rods 15 that hang downward and carry a bottom ring 16 upon which rests the inner edge of the bottom oor 17 said Hoor is funnel shaped and incloses, on the underside, the compressed air compartments 18 that are inclosed on their upper side by a porous lower deck 19 constructed of material analogousto that of the porous upper deck 5 and arranged within the wall 9, which also forms the outer wall of the sub-compartments 18 and of the inner chamber 2O which is formed between the porous lower deck 19 and the upper floor 8. Apertures 21 at intervals around the wall 9 give access to the cham-- ber 2O from outside the apparatus.

The upper floor `8 is supported by angleirons 22 fastened to the annular wall 9.

External to and spaced from said annular wall 9 is an annular ring of sheet-iron or other suitable material forming a froth skimming wall 23 extending from a level above the top of the annular wall 9 downward to and below the level of the upper edge of the lowerV porous -deck 19; and within said annular ring and between it and the wall 9 there is formed an air trunk 24 and a froth channel 25, separated by an annula inwardly sloping porous floor 26 that connects with wall 9 just below orices 27 that are provided through the wall 9 and that communicate between the froth channel 25 and the inner chamber 20, so that the contents of thefroth channel 25 may readily flow from the bottom of said channel into the inner chamber 2O and be distributed at the upper periphery of said lower deck, thus to be subject to the frothing action of air forced through the lower porous deck 19.

Compressed air is supplied from air trunk 24 to the compartments 18 through perfora-V tions 28 through wall 9.

The outlet through the porous floor 26 is sufliciently free to allow enough air to pass therethrough to maintain the frothy conditions of the contents of the channel.

The bottom of the air trunk 24 is formed by an annular horizontal ring 29 resting upon columns 30 that afford the main outer support for the apparatus. Said air trunk 24 is connected by a pipe 31 through a valve 32 with the compressed air supply pipe 13 and is also connected through perforations 28 in the wall 9 with the air compartments 18 beneath the porous lower deck 19. Apertures 33 through the joists 34 afford free communication of the air between the various compartments 18. Like orifices 35 through the joists 6 aEord free communication of the air between the compartments 7.

External to the skimming wall 23 that forms a place of separation where the concentrates carrying portion of the froth is skimmed from the remaining froth which may be wholly barren or nearly so, there are arranged one or more collecting launders 36 to receive the concentrates that are carried by the froth flowing over the skimming wall. Said collecting launders are constructed as hoppers discharging through pipes 37 into the concentrates launder 38.

Centrally arranged at the lower annular end of the Hoor 19 is a central annular skimming wall 39 terminating at a distance above the lower end of the deck 19, there being a passage 40 at the level of the lower end of said deck to allow the tailings from said lower deck to flow into a pipe 41, and thence into the tailings launder 42, through which it is discharged from the machine. Connected to the top of the lower skimming wall 39 is the concentrates chute in the form y of a funnel 43 discharging through the spout 44 into the concentrates launder 38.

The passage 40 may be formed as a narrow open space between the bottom of the lower skimming wall 39 and the lower deck 19 and the flow through such passage may be froth into the funnel 43 thereby to insure saving all the metalliferousl particles that may have passed out the lower deck.

In practical operation the pulp distributed to the apex of the upper porous deck '5v is immediately frothed by the ascending air, and at the same time such air has a tendency to maintain the surfaces of the metallic mineral particles in a dry condition, and therefore making said particles highly subject to adherence upon the films of the froth bubbles. The fluid mass gravitates toward the rim of the upper porous deck, but does not lose its frothy character, and flows as a froth into the froth channel 25 filling the same, and still subject as a froth to the dryingl action of air emitted from the air channel 24 through the porous `bottom 26 of the froth channel 25 with the result that the surface of the froth is crowded over the skimming wall into the collecting launder 36 arranged to receive the same, and there, the froth, being no longer subject to the action ofthe compressed air, subsides and the resulting liquid carries the mineral particles on into the concentrates launder.

Meanwhile the tailings from. the froth channel 25 flow in a thin sheet down the lower porous deck where they are subject to the frothing action as before and the upper surface of the resulting froth flows over the lower skimmin wall 39 and thence to the launder 38 while the tailings flow out through the tailings outlet 40 to the tailings launder '42.

Throughout the process, air under pressure sufficiently high to cause its even distribution through the porous bodies 5, 19 and 26 is forced into the various compartments and coming up i through the porous deck forming the tops of the compartments 7 converts the pulp layer into a thicker layer of froth with concentrates forming on it. The froth on the top deck is held back suiciently by the skimming wall 23 to cause the mineral bearing top layer to iow over into the collecting launder.

The pulp mixture in passing through the machine is continually maintained as froth, as it overlies a porous surface through which is constantly passing evenly distributed air under pressure. I

The outlet through porousfloor 26 may be of less capacity than through wall 9 so that air pressure in the air trunk 24 may be somewhat higher than that in the air compartment 19 of the lower deck 'on account of having to maintain the greater depth of froth above such floor.

The pressures delivered through air pipes 1 1 and 31 may be regulated by adjusting,

the valves 12 and 32 and may range from a few ounces up to live or six pounds more or less.

rlvhe porous deck may be of any suitable diameter, as for instance eight feet more or less, and may be of any suitable thickness, as for instance one and a half inchesv thick, more or less but the dimensions and shape may be changed without departing from the broad spirit of the invention.

The air may be delivered to pipe 13 in a dehydrated condition by any well known method as by subjecting the compressed air to freezing temperatures and thus extract ing the moisture therefrom before Vit reaches such pipe. It is not usually necessary, however that the air shall be thus dried in order to get satisfactory results.

I claim 1. The method of recovering metalliferous minerals from ore pulp by notation which consists in converting the'pulp to a frothy condition and subjecting the froth to the action of drying currents of air and thereby maintaining-the whole body of pulp in such frothy condition; collecting the froth in a body of considerable depth and causing the superficial froth to flow over such froth body thereby removing the metalliferous mineralfrom the gangue.

y2. In a flotation method of recovering metalliferous minerals from ore pulp the step set forth which consists in converting the pulp into froth and applying' finely divided currents of dry air vdirectly beneath the frothy pulp and thereby continuously drying the surfaces of the mineralized particles so as to maintain their adhering qualities and floating the same over the froth surface to a place of separation.

3. The method of recovering metalliferous minerals from ore pulp which consists in f converting the' pulp into froth; subjecting the froth to the uplifting and drying action of finely divided air currents; causing the froth to flow toward a place of separation meanwhile spreading the froth over a wider area, at the same time deepening the body of froth Vand subjecting said deepened body to the continuous action of such air currents and forcing the surface froth to separation.

4. The method of recovering metalliferous minerals from ore pulp which consists in converting the pulp into froth; subjecting the froth to the uplifting and drying action of. finely divided air currents; causing the 'froth to flow toward a place of separation meanwhile spreading the froth over a wider area, at the same time deepening. the body of froth and subjecting said deepened body to the continuous action of such air currents forcing the sun'face froth to separation; drawing olf frothy material frombelow the surface of said deepened froth body andthe frothy material thus being'drawn off.

5. The apparatus' for recovering metalliferous minerals from ore pulp treated with 10 the deck; means to force air up through such deep froth body; and means to draw tailings 0H at the bottom of such deep froth body.

In testimony whereof, I have hereunto set my hand at Los Angeles, California, this 15 1st day of March 1915.

GEORGE CRERAR. In presence of- JAMES R. TowXsEND, ESTELLA HILL. 

